2230
Macromolecules 1998, 31, 2230-2235
Synthesis of Conductive Nanocomposites by Selective In Situ
Polymerization of Pyrrole within the Lamellar Microdomains of a Block
Copolymer
M. C. de Jesus† and R. A. Weiss*,†,‡
Polymer Science Program and Department of Chemical Engineering, University of Connecticut,
Storrs, Connecticut 06269-3136
S. F. Hahn
Central Research, The Dow Chemical Company, Midland, Michigan 48674
Received November 13, 1997; Revised Manuscript Received January 23, 1998
ABSTRACT: Electrically conductive nanocomposites were prepared by a selective in situ polymerization
of pyrrole within the lamellae ionomeric microdomains of sulfonated poly(styrene-b-(ethylene-altpropylene)), SEP, diblock copolymers. A conductivity of 10-3-10-1 S/cm was achieved parallel to the
film surface for PPy concentrations from 5 to 11 wt % PPy. Although the microstructure of the block
copolymer was not purposefully aligned, the conductivity was anisotropic, varying 1-2 orders of magnitude
parallel and normal to the plane of the composite films. The in situ polymerization of pyrrole in the SPS
microphase did not disrupt the texture of the block copolymer microstructure, though the interphase
between the polystyrene and rubber lamellae became more diffuse. Incorporation of PPy also improved
the modulus of the block copolymer above the Tg of the ionomer microdomains.
Introduction
One approach for exploiting the intrinsic electrical
conductivity of polymers such as polypyrrole, polythiophene, or polyaniline and overcoming their poor
mechanical properties is to blend them with a nonconductive polymer. Over the past decade, many research
groups have prepared conductive blends or composites
by employing an in situ polymerization of the conductive
polymer within a preformed polymer host using that
approach, and that subject was recently reviewed.1
A variation on the blend theme is to use the mesophase texture of a block copolymer as a template for
directly preparing an anisotropically conductive material. The key feature of that approach is that selfassembly of a block copolymer provides nanometer-size
domains with well-defined geometries and spatial register, e.g., cubic packed spheres, hexagonal packed
cylinders, and alternating lamellae.2 The incorporation
of conductive particles or the in situ polymerization of
a conductive polymer within one of the microphases of
a block copolymer produces a conductive nanocomposite.
Ishizu et al.3,4 prepared anisotropically semiconducting films by exposing a poly(styrene-b-2-vinylpyridine)
diblock copolymer (S2VP) with oriented lamellar microdomains to alkyl halide vapors, and they observed
an 8 order of magnitude difference in the conductivity
parallel and perpendicular to the plane of the resultant
film. They also introduced colloidal silver into quarternized 2VP lamellae by the reduction of silver iodide.5
Similarly, Stankovic et al.6 incorporated iodine into a
S2VP block copolymer, but they observed no relationship between the conductivity and the orientation of the
block copolymer. Ishizu and co-workers7 also used
cross-linked S2VP films containing Cu(II) complexed to
the 2VP for an in situ polymerization of pyrrole.
Because the Cu(II) oxidant was only present in the 2VP
†
‡
Polymer Science Program.
Department of Chemical Engineering.
microphase, polypyrrole (PPy) was restricted to the 2VP
lamellar microdomains, and those materials had an
electrical conductivity as high as 10-1 S/cm and high
anisotropic conductivity. Smith et al.8 prepared highly
ordered nanocomposites containing poly(p-phenylenevinylene), PPV, another conductive polymer that exhibits
photoluminescence, by polymerizing lyotropic liquid
crystals to form a highly ordered matrix phase. The
resulting hexagonally ordered PPV nanocomposite exhibited significantly enhanced photoluminescence.
Radhakrishnan and Saini9 polymerized pyrrole in a
poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer using FeCl3 as the oxidant and dopant. Although they claimed that the PPy was preferentially
incorporated in the polybutadiene microdomains, the
data presented in their paper do not support that
conclusion. Their assertion of intercalation of PPy in
the rubber domains was based upon optical microscopy
and wide-angle X-ray diffraction, WAXD, but optical
microscopy cannot resolve the 10-100 nm-sized microdomains that are characteristic of a block copolymer
microstructure and WAXD probes a size scale 1-2
orders of magnitude smaller than that for the polybutadiene microdomains. Their optical micrographs
clearly show macroscopically phase-separated PPy distributed throughout the polymer sample, which is
typical of the product one obtains from an in situ
oxidative polymerization of pyrrole in a polymer matrix
that does not specifically interact with PPy.
The objective of the research described in the present
paper was to preferentially incorporate PPy into the
glassy microdomains of a thermoplastic elastomer, i.e.,
a poly(styrene-b-(ethylene-alt-propylene)) (SEP) triblock
copolymer. The preferential selectivity of the polystyrene microphase for the oxidant, which does not appear
to be achieved in the work by Radhakrishnan and
Saini,9 was accomplished by lightly sulfonating the
polystyrene blocks. That sufficiently altered the polarity of the polystyrene, so that aqueous solutions of the
S0024-9297(97)01678-1 CCC: $15.00 © 1998 American Chemical Society
Published on Web 03/07/1998
Macromolecules, Vol. 31, No. 7, 1998
Conductive Nanocomposites via Pyrrole Polymerization 2231
Table 1. Electrical Conductivity of HSEP/PPy Composite Filmsa
sample
wt % PPy
vol % PPy in
SPS domains
σ1 (4-pt probe) (S/cm)
σ2 (2-pt probe) (S/cm)
σ1/σ2
5.6 HSEP35.6
7.0 HSEP35.6
4.7 HSEP50.4
6.0 HSEP50.4
4.8
6.4
11.0
10.0
9.9
12.8
15.1
14.0
7.03 × 10-3 (0.0457)b
3.38 × 10-4 (0.0174)
4.42 × 10-2 (0.0006)
1.74 × 10-2 (0.0101)
4.4 × 10-5 (0.6987)c
2.9 × 10-5 (0.2828)
4.7 × 10-4 (1.7022)
3.82 × 10-4 (1.8243)
160
12
94
46
a Calculated from wt %, assuming all the PPy is in the SPS microphase and F
3
3 b
SPS ) 1.06 g/cm and FPPy ) 1.35 g/cm . The number in
parentheses is the standard deviation of five measurements. c The number in parentheses is the standard deviation of three measurements.
oxidant and the pyrrole monomer preferentially partitioned into the sulfonated polystyrene (SPS) microdomains and not into the rubber (EP) microphase. As
a result, PPy formation was restricted to the SPS
microdomains, which for a lamellar block copolymer
texture produced a material in which nanometer-sized
lamellae of conductive PPy/SPS were separated by a
nanometer-sized EP rubber lamellae.
Experimental Details
The SEP diblock copolymers were synthesized by sequential
anionic polymerization of styrene and isoprene, followed by
hydrogenation of the polydiene block. Because the polyisoprene microstructure contained essentially 1,4-additions, the
resulting rubber block in the hydrogenated SEP was essentially an alternating ethylene-propylene copolymer. The
details of the polymerization and hydrogenation reactions, as
well as a complete characterization of the block copolymer
texture, are given elsewhere.10 Two different block copolymers
were used: one with Mn ) 52, Mw/Mn ) 1.03 and containing
35.6 wt % PS and one with Mn ) 52, Mw/Mn ) 1.04 and
containing 50.4 wt % PS, hereafter referred to as SEP35 and
SEP50, respectively. Both exhibited alternating lamellar
microstructures in films that were either cast from solution
or melt pressed.
The SEP block copolymers were sulfonated using acetyl
sulfate following the procedure described by Weiss et al.11,12
The sulfonation level of the polymer was determined by
titration of the sulfonic acid derivatives in a mixed solvent of
toluene/methanol (90/10 v/v) to a phenolphthalein end point.
Films of sulfonated block copolymers, ca. 200 µm thick, were
prepared by slowly evaporating the solvent over a period of 6
days from a partially covered Petri dish containing a 10 wt %
solution of the polymer in a toluene/methanol (90/10 v/v) mixed
solvent. The cast films were removed from the glass dish and
dried at 50 °C under vacuum for at least 48 h and then at 100
°C for 24 h.
The sulfonated diblock copolymers are hereafter denoted as
x.yHSEPz, where x.y is the degree of sulfonation of the
polystyrene (PS) blocks (mol % styrene sulfonated), H indicates
the sulfonic acid derivative, and z denotes the nominal wt %
styrene, i.e., 35 or 50. For example, 4.7HSEP35 represents
the sulfonic acid derivative of a sulfonated diblock copolymer
containing 35.6 wt % PS and a degree of sulfonation of 4.7
mol %.
The in situ polymerization of pyrrole in the HSEP films was
carried out using the procedure described in ref. 13. The films
were first immersed in a 0.5 M aqueous solution of pyrrole for
24 h and then immersed in a 1.0 M aqueous solution of FeCl3
for another 24 h. When the pyrrole polymerization occurred,
the films acquired the characteristic black color of PPy. The
HSEP/PPy composite film was removed from the FeCl3 solution, washed with distilled water, and dried at 50 °C under
vacuum for 48 h. The amount of PPy incorporated in the film
was determined gravimetrically.
Dynamic mechanical properties were measured with a
Polymer Laboratories MkII dynamic mechanical thermal
analyzer (DMTA) using a tensile fixture, a frequency of 1 Hz,
a temperature range of -150-200 °C, and a scanning rate of
3 °C/min. Thermal stability of the films was measured with
a Perkin-Elmer thermogravimetric analyzer, model TGA-7,
using a nitrogen atmosphere and a heating rate of 10 °C/min.
The surface morphology of the films was characterized with
an AMR model 1200B scanning electron microscope (SEM)
equipped with an EDAX 9100/08 detector and a DX series
workstation. EDAX spectra were obtained on samples fractured after immersion in liquid nitrogen. The block copolymer
texture was determined with a Philips EM300 transmission
electron microscope (TEM) operated at an accelerating voltage
of 80 kV. Ultrathin sections were prepared by microtomy
using an ultramicrotome LKB Ultratome V equipped with a
diamond knife. The sections were collected on Formvar and
carbon-coated copper grids and stained at room temperature
by exposure to the vapors of a 0.5% aqueous ruthenium
tetroxide (RuO4) solution for 5 min. RuO4 preferentially stains
the polystyrene, thereby enhancing the electron contrast
between the two microphases of the block copolymer. Smallangle X-ray scattering (SAXS) measurement experiments were
made with a Bonse-Hart camera, equipped with a twochanneled-cut germanium crystal, a scintillation counter and
using Cu KR radiation. All scattering profiles were corrected
for sample thickness and absorption.
The dc conductivity of the films (σ1) was measured by a
conventional four-point probe technique in which the electrodes were separated by 0.6 mm; a slight pressure, just
enough to ensure a good contact between the film and the four
probes, was applied. The bulk conductivity normal to the
surface of the film (σ2) was measured by a two-point probe
technique in which the electrodes were firmly pressed against
the opposite sides of the film.
Results and Discussion
The HSEP-50 block copolymer ionomer had microstructures consisting of alternating SPS and PEP
lamella with a long-spacing determined by SAXS of ∼50
nm.10 The polymerization of pyrrole occurs only in the
presence of oxidant (FeCl3). Because sorption of the
aqueous pyrrole and oxidant solutions is much more
favorable in the hydrophilic SPS microdomains, as
opposed to the hydrophobic rubber microdomains, it was
expected that the block copolymer texture would serve
as a template for the polymerization and organization
of the PPy preferentially within the SPS microdomains.
The HSEP/PPy composites produced are summarized
in Table 1. In general, the PPy production increased
with increasing polystyrene composition and sulfonation
level, which can be attributed to the increased water
sorption by the films as the number of sulfonate groups
and the volume fraction of the SPS microphase increased. Incorporation of the PPy into the block copolymer had no effect on the thermal stability of the block
copolymer. TGA thermographs for the sulfonated diblock
copolymers and their composites (not shown) were
similar, although the composite exhibited a slower
weight loss with increasing temperature that was
probably due to the higher viscosity of the composite.
The effect of PPy concentration on the electrical
conductivity parallel (σ1) and perpendicular (σ2) to the
film surface is shown in Figure 1 (note that the lines
drawn in Figure 1 serve only to guide the eye and have
no real significance). The number of materials studied
was not sufficient for determining if there were any
intrinsic differences in the conductivities for the com-
2232 de Jesus et al.
Figure 1. Electrical conductivity of PPy/HSEP nanocomposites: (0) σ1; (O) σ2.
posites prepared from the two different block copolymers. However, because the microstructures of all the
materials were similar, i.e., alternating PPy/SPS and
EP lamellae, it was assumed that the composition of
the block copolymer had a minor effect if any on the
electrical properties of the composites.
Both σ1 and σ2 increased with increasing PPy concentration, and the conductivity of the composite films
was in all cases anisotropic, ranging from 1 to 2 orders
of magnitude difference parallel and perpendicular (i.e.,
σ1/σ2) to the film surface. The electrical anisotropy
arises from the fact the PPy is preferentially incorporated in the SPS lamella microdomains (the evidence
for which will be discussed later in this paper), which
for an air-dried film should be preferentially aligned
parallel to the film surface. The composite microstructure consisted of conductive SPS/PPy layers separated
by nonconducting PEP rubber layers. An ideal microstructure in which the layers are well aligned parallel
to the film surface would be expected to have a high
conductivity in the plane parallel to the film surface,
but little conductivity, i.e., be insulating, perpendicular
to the surface. The data in Table 1 and Figure 1,
however, show that relatively high conductivity occurred
in both planes, which indicates that a conductive PPy
pathway was present not only parallel to the film
surface but also normal to it. The relatively low
electrical anisotropy was due to imperfect alignment of
the lamella parallel to the surface of the film. This
provided a conductive path both normal to the film
surface and in the plane of the film. Still, the higher
σ1 values suggest that there was some preferred orientation of the lamella parallel to the film surface. More
details on the microstructure of the nanocomposites are
discussed later in this paper.
Conductivity in these composite films occurred at
relativity low concentrations of PPy, less than 0.05 mass
fraction based on the total mass of the composite (the
volume fraction of PPy, though not shown in Table 1,
is within 10% of the mass fraction). The percolation
threshold concentration for conductivity for a random
dispersion of conductive spheres in a polymer is 0.16
volume fraction.14 For rodlike conductive particles, the
threshold concentration is lower,15,16 though still greater
than 0.05 volume fraction. However, nonrandom distributions of a conducting phase in a mixture of conducting and insulating materials can result in conduc-
Macromolecules, Vol. 31, No. 7, 1998
Figure 2. EDAX of the fracture surface of the nanocomposite
of 10.0 wt % PPy in 6.0HSEP50: (a) at the surface of the film;
(b) at a position intermediate between the surface and center
of the film; (c) at the center of the film.
tivity at substantially lower threshold concentrations.17-19
The unusually high conductivity of the PPy/block copolymer composites at a seemingly low PPy concentration is due to the preferential intercalation of PPy in
only the SPS microdomains. As a result, the actual
concentration of the conducting polymer within the
conducting microphase is much higher, 10-15%, than
that based on the total composite mass; see the third
column in Table 1.
The conductivity values for the composite film containing 6.4 wt % PPy (see Figure 1) were low compared
with the other samples. That was a consequence of the
poorer organization of the lamellar microstructure in
that sample. Because the PPy is contained only within
the SPS domains, the conductivity is sensitive to the
texture of the block copolymer microstructure and the
long-range order of the microphase-separated domains.
EDAX analyses indicated that Cl- was the counterion
for the protonated PPy and no Fe was detected in the
composites, Figure 2. The latter result confirmed that
any excess FeCl3 oxidant and the FeCl2 byproduct of
the pyrrole polymerization reaction were effectively
removed from the composite during the washing process. EDAX measurements of the cross-section of the
film near the surface and near the center indicated,
however, that the Cl- concentration (see the Cl KR peak
in Figure 2), and presumably the PPy concentration as
well, was higher near the surface.
The inhomogeneous distribution of PPy through the
film thickness is not surprising in that the pyrrole
polymerization reaction was accomplished by diffusing
the oxidant into a pyrrole-swollen film. Because the
oxidant diffuses from the surface into the film and the
polymerization reaction occurred where both oxidant
and pyrrole were present, the polymerization actually
occurs from the surface of the film inward. The S KR,
which is due to the sulfonate groups of the ionomer
microphase, is suppressed in the EDAX of the surface
region, which indicates a relatively high concentration
of PPy at the surfacesthat is, a low concentration of
the block copolymer. One explanation for the PPy
gradient in the film is that polymerization of pyrrole
retarded or inhibited the diffusion of the oxidant solution into the film, so that the reaction did not occur
Macromolecules, Vol. 31, No. 7, 1998
Conductive Nanocomposites via Pyrrole Polymerization 2233
Figure 4. TEM microgaph of cross-section of films of (a)
5.6HSEP35.6 and (b) nanocomposite of 4.8 wt % PPy in
5.6HSEP35. The dark regions are the SPS microphase.
Figure 3. SEM micrograph of the surface of a nanocomposite
film of 4.8 wt % PPy in 5.6HSEP35.
uniformly throughout the film. This is manifest by a
depletion of PPy at the center of the film. The PPy
concentration in the film generally increased with
increasing sulfonation level and volume of the sulfonated microphase, and EDAX indicated that more PPy
penetrated into the core of the film as the total PPy
concentration increased.
Figure 3 is an SEM micrograph of the surface of the
5.6HSEP35.6 composite (4.8% PPy). The micrograph
clearly shows 5-20 µm PPy particles on the surface,
though they appear to be embedded in the film rather
than simply deposited on the surface. There was no
noticeable debris on the surface by visual observation
of the films, and the films were not freely marking.
Those observations are consistent with PPy particles
being embedded in the polymer. No PPy phase was
observed by SEM in fracture surfaces of the film, other
than at the film surface. Because the EDAX analyses
indicated that the PPy was present in the core, as well
as on the surface, it would appear that PPy was
incorporated in the core on a size scale smaller than the
resolution of the SEM (<0.1 µm). The PPy particles
observed on the surface of the composite films may
contribute in part to the electrical anisotropy. However,
the PPy surface layer cannot explain the relatively high
conductivity (10-5-10-3 S/cm) normal to the film surface. If the PPy were homogeneously dispersed within
the bulk of the film, the concentration of PPy in the bulk
phase would be too low to provide a percolation pathway
for conductivity, and the conductivity should be <10-8
S/cm. The only way that conductivity could occur
normal to the film surface in these samples is if the PPy
were concentrated within one of the microphases.
A comparison of TEM micrographs before and after
the in situ polymerization of pyrrole in the 5.6HSEP35.6
block copolymer indicated that PPy was intercalated
within the 10-20 nm thick SPS lamellae of the block
copolymer, Figure 4. The PPy/5.6HSEP35.6 sample
contained 4.8% (wt) PPy. The dark microphase in
Figure 4 corresponds to the RuO4-stained SPS lamellae
and the lighter domains are the EP rubber lamellae. It
is clear that the in situ polymerization of pyrrole did
not perturb the general block copolymer texture, though
the interface between the lamellae is not as sharp in
the composite as in the neat block copolymer. Evidence
for the preferential segregation of the PPy into the SPS
domains can be inferred from the preservation of the
contrast between the microphases in the TEM micro-
Table 2. Microstructure Period for the Block Copolymer
and Thickness of the SPS Lamellae Measured by SAXS
and TEM
SAXS
sample
PPy
wt %
φ2
5.6HSEP35.6
5.6HSEP 35.6
7.0HSEP35.6
7.0HSEP35.6
4.7HSEP50.4
4.7HSEP50.4
6.0HSEP50.4
6.0HSEP50.4
0
4.8
0
6.4
0
11
0
10
0.334
0.355
0.334
0.367
0.480
0.519
0.480
0.520
TEM
q
D
(nm-1) (nm)
L
(nm)
D
L
(nm) (nm)
0.111
0.114
0.141
0.142
0.145
0.144
18.94
19.56
14.9
16.18
20.74
22.68
32.6
33.7
28.1
26.4
24.7
28.1
24.7
28.1
56.7
55.1
44.6
44.1
43.2
43.7
10.9
12
9.4
9.7
11.9
14.6
11.9
14.6
graphs in Figure 4. Since RuO4 is expected to react with
the double bonds of the PPy, as well as with the styrene,
the EP microphase should also be stained if it contained
appreciable PPy. The swelling of the SPS lamellae also
indicated that the PPy was in those microdomains.
The characteristic distance of the lamellar texture,
measured from the center-to-center spacing of two
consecutive SPS lamellae, increased upon incorporation
of PPy into the block copolymer; see Table 2. Within
the experimental error associated with measuring lamellae thickness from the micrographs, an increase in the
thickness of the SPS lamellae accounted for the increased domain spacing; see Table 2. Similar results
were obtained from TEM analysis of the other composites, though in some cases, the long-range order of the
lamellae was not as pronounced as for the sample in
Figure 4. However, in each case, except for the swelling
of the SPS domain thickness and the development of a
more diffuse interface between lamellae, the block
copolymer textures of the composites were comparable
to those of the original block copolymer film.
Figure 5 is a TEM micrograph of a cross-section of a
nanocomposite of 6.4 wt % PPy in 7.0HSEP35.6. This
was the sample that had the lowest anisotropy of the
conductivity; see Figure 1. The reason for the high σ2
is evident from the poor alignment of the lamellae
microphases in this sample (cf. Figures 4 and 5), which
provide a conductive PPy/SPS pathway normal, as well
as parallel, to the surface of the film.
A SAXS profile for the nanocomposite of 5.6HSEP35.6
containing 4.2 wt % PPy is shown in Figure 6. Six
scattering peaks are visible (see arrows), and the ratio
of the scattering vectors, q, of the maxima (q ) 4π(sin
θ)/λ, where θ is half the scattering angle and λ is the
X-ray wavelength) correspond approximately to 1:2:3:
4:5:6, which is characteristic of a lamellar structure.
Some uncertainty in the position of the scattering
maxima with respect to the first maximum arises from
the desmearing procedure, which probably explains the
2234 de Jesus et al.
Macromolecules, Vol. 31, No. 7, 1998
Figure 7. Dynamic modulus vs temperature for films of (O)
4.7HSEP50 and (0) nanocomposite of 11 wt % PPy in
4.7HSEP50.
Figure 5. TEM micrograph of cross-section of a nanocomposite film of 6.4 wt % PPy in 7.0HSEP35.6.
Figure 6. SAXS profile a nanocomposite film of 4.2 wt % PPy
in 5.6HSEP35.6. The incident beam was normal to the surface
of the film.
deviation of the peak positions from integer multiples
of q from the first maximum. The third- and sixth-order
maxima in Figure 6 are suppressed as a consequence
of selective interference with the particle shape factor
of the lamellar stacks, which suppresses the SAXS
maxima of ∼1/wSPS, where wSPS is the mass fraction of
the ionomeric block.20 SAXS profiles corresponding to
lamellar microstructures were also obtained for the
other block copolymer and nanocomposite films used in
this study, except in some cases only the first and second
maxima were observed due to poorer development of the
texture and less long-range order in those films.
The position of the first-order maximum in the SAXS
curve, q*, provides an estimate of the period of the
lamellar structure, D, by applying Bragg’s law:
D ) 2π/q*
(1)
The thickness of the ionomer lamellae, L, was calculated
from
L ) Dφ2
(2)
where φ2 is the volume fraction of the sulfonated block.
The results for these two calculations are given in Table
2 for the neat block copolymers and the composites. φ2
for the composite films was calculated by assuming that
all the PPy was in the SPS microdomains and that the
density of the PPy-containing ionomer phase was a
weighted average of the densities of the two polymers.
Although the absolute value of D and L calculated from
the SAXS and TEM data differed, in both cases the
lamellae thickness of the SPS lamellae increased with
incorporation of PPy. The discrepancy of the lengths
measured by the two techniques may be partially due
to some of the assumptions inherent in the sizes
calculated from the SAXS data and to the errors in
measuring the lamellae thickness off the micrograph.
The dynamic storage modulus, E′, is plotted against
temperature in Figure 7 for 4.7HSEP50 and a composite
containing 11 wt % PPy. The two transitions, at ca. -50
°C and ca. 110 °C, are the glass transition temperatures
of the PEP and SPS microphases, respectively. The Tg
of the SPS phase in the nanocomposite was slightly
lower than that for the neat block copolymer, which may
be due to either plasticization by residual water or
disruption of the hydrogen-bonded network of sulfonic
acid groups by intermolecular hydrogen bonding of the
PPy and the ionomer.
The major influence of the incorporation of PPy on
the viscoelastic behavior of the block copolymer ionomer
was to increase E′ above the Tg of the SPS microphase.
That was a result of the rigid PPy serving as a
reinforcement for the block copolymer melt. The modulus enhancement at elevated temperature was more
than 1 order of magnitude, and no viscous flow of the
block copolymer composite was observed up to 200 °C.
A similar enhancement of E′ above Tg by the incorporation of PPy by an in situ polymerization of pyrrole was
previously reported for an SPS ionomer.13 The other
PPy-containing block copolymers exhibited similar behavior, though the magnitude of the reinforcement
above Tg of the SPS microphase depended upon the PPy
concentration. The differences in the modulus of the
two materials below Tg of the PEP microphase, i.e., T
< -50 °C, are probably due to slippage of the glassy
film in the test fixture and are not considered significant.
Conclusions
Ionomeric block copolymers, sulfonated poly(styreneb-(ethylene-co-propylene), with alternating lamella mi-
Macromolecules, Vol. 31, No. 7, 1998
crodomains were used as templates for the in situ
polymerization of pyrrole. The reaction locus for the
polymerization was the hydrophilic sulfonated polystyrene microdomains, which were preferentially swollen
by aqueous solutions of the pyrrole monomer and the
FeCl3 oxidant.
Incorporation of PPy did not affect the alternating
lamellae microstructure of the block copolymer, though
the boundaries between the polystyrene and rubber
microphase became more diffuse. Both the surface and
bulk conductivity were dependent upon the amount of
PPy incorporated into the system; conductivity parallel
to the film surface varied from 10-3 to 10-1 S/cm as the
PPy concentration varied from 5 to 11 wt %. The
conductivity normal to the surface was generally 1-2
orders of magnitude lower. Presumably, samples with
higher anisotropy of the conductivity could be prepared
if the alignment of the microstructure were improved.
Incorporation of PPy into the block copolymer also
improved the modulus of the melt above the Tg of the
SPS microdomains and suppressed viscous flow of the
composite.
Acknowledgment. This work was partially funded
by grants from the Army Research Office (Grant DAAH
04-94-G-0082) and by Connecticut Innovations Inc.
(Grant 95G022). We are grateful to Dr. Benjamin Hsiao
at the DuPont Central Research and Development
Laboratory for the SAXS results and Prof. Marie Cantino and Dr. Lamia Khairallah of the Electron Microscopy Laboratory in the Department of Physiology and
Neurobiology at the University of Connecticut for the
TEM micrographs.
Conductive Nanocomposites via Pyrrole Polymerization 2235
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(4) Ishizu, K.; Yamada, Y.; Saito, R. ; Kanbara, T.; Yamamoto,
T. Polymer 1992, 33, 1816.
(5) Ishizu, K.; Yamada, Y.; Saito, R. ; Kanbara, T.; Yamamoto,
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